|By Julien Pretot

|By Julien Pretot

GRENOBLE, France (Reuters) - The Tour de France will go down to the wire and will be decided in the last mountain stage on Thursday at the end of another grueling ride, three-time champion Greg LeMond said on Tuesday.

The peloton will tackle the punishing ascents of the Croix de Fer, Col du Telegraphe and Col du Galibier before a downhill finish in Serre-Chevalier in Wednesday's 17th stage.

But the 18th stage will be the crucial one, ending up the lung-busting Col d'Izoard, where the "first big battle of the climbers" will be staged according to LeMond, a Tour winner in 1986, 1989 and 1990.

"It will come down to Izoard, it will be the first big battle for climbers to win the Tour," the American, who is on the Tour as an analyst for Eurosport, said in his daily chat with Reuters.

"We've never seen a really all-out day of racing since the start. In Peyragudes, they just raced in the last 500 meters."

Wednesday's downhill finish, with a possible headwind, would make it hard for a lone rider to go all the way to the line.

"It's not as explosive as you think (on Wednesday). The Croix de Fer is really hard and the Galibier is really long, but it will be hard to put time into Froome," said LeMond.